Vehicle gearboxes are usually controlled or shifted by an actuating device within the driver's area of reach. Operating elements like a gearshift or a selector lever are positioned, for example, between the front seats are regularly used.
The constructional and ergonomic requirements for such actuating devices or selector levers are thereby numerous. In order, for example, to give the driver a realistic feeling for transmission operation for reasons of safety and ergonomics, it is required of actuating devices of this type that both optical as well as clearly haptic or tactile feedback is sent to the driver. The driver should be expected to infer during operation of the shift selector level the shifting procedure actually occurring in the transmission from this. It should also be possible for the driver to be able to determine intuitively by a look or grasping of the selector lever the shifting status at the moment.
It is thus desirable to impart to the driver a clear optical and haptic feedback about the current state of the transmission or the driving gear actually engaged based on the momentary position or angular position of the selector lever.
In the case of mechanical transmission actuation or a mechanical clutch between the selector lever and the gearshift—for example by means of a cable pull or a linkage—the selector lever position always agrees with the actual gear position because of the mechanical clutch. Since mechanically operated gearshifts are in general multi-stable (the gear shift position is stable in several or all positions and does not change independently), the associated selector lever is also multi-stable and this always remains in the position set by the driver.
As a result, the driver can, on the one hand, conclude from the respective selector lever position the actual shift status of the gearbox or recognize, based on the selector lever position, the gear respectively engaged in the transmission and, on the other hand, rely on the fact that the selector lever position will not deviate from the actual shift status of the gearbox.
In the case of the increasingly used electric actuation or the shift-by-wire operation of the gearbox, no mechanical clutch exists anymore between the actuating device or the selector lever in the passenger compartment and the vehicle transmission in the motor area. Moreover, the transmission of shifting commands from the actuating device to the vehicle transmission occurs in the case of “shift-by-wire” transmission almost exclusively by means of electrical or electronic signals, and thereafter an almost electro-hydraulic conversion of the shift commands. That partially applies for modern gearboxes, especially for the current generations of automatic transmissions which are almost completely remotely controlled by actuators.
In the case of a shift-by-wire operated gearbox, the missing mechanical connection between the gearbox actuators and the selector lever can, however, result in the selector lever position no longer matching the shift status of the gearbox under certain framework conditions or in the case of error.
Thus modern automatic transmissions feature a so-called auto-P function which ensures that when leaving the vehicle, the parking lock is always engaged in the transmission in order to prevent a rolling away of the unattended vehicle. The auto-P function which goes into action, for example, when the ignition key is withdrawn or upon leaving the vehicle, in other words ensures the automatic setting of the parking lock in the transmission independent of the actual drive gear selected on the selector lever. The parking lock is also then set by the auto-P function of the transmission or the vehicle, when the selector lever is actually left by the driver in the neutral position or in another drive gear position.
In this case, the selector lever position no longer agrees with the actual shift status of the transmission. Upon returning to the vehicle or when attempting to start the vehicle, both unsatisfactory optical as well as haptic information is conveyed to the driver. Once the selector lever position is recognized, the driver assumes that the transmission is, for example, in the neutral position or in a drive gear position, while the transmission, on the other hand, actually has the parking lock set. This discrepancy between the selector lever position and the transmission status can thus result in an undesired faulty operation, in improper inferences by the driver and thus also to situations critical to safety; or else an additional signal device must be provided for the driver which signals the driver in the case of the parking block set by the auto-P that the vehicle must first be started, if the selector lever is manually brought into the park position.
An attempt was made to so counter the stated problem in that the selector lever of a shift-by-wire gearbox has been constructed as a mono-stable actuating device. In other words, this means such a selector lever constructed in a mono-stable manner always returns to the same middle position after each operation. In connection with a mono-stable selector lever, the feedback about the actual shift status of the gearbox remains exclusively entrusted to a separate display, for example, by means of light diodes. On the other hand, with a mono-stable selector lever, the possibility of conveying to the driver either optic or haptic feedback about the shift status of the gearbox is lacking. Furthermore, the realization of the mechanical shift logic and the necessary shift locks, like for example the so-called key-lock and shift-lock locks, are at least difficult with a mono-stable selector lever and require expensive actuators for the selective blockage of the selector lever.
The safety function known as the so-called key-lock system results, for example, in a blockage of the selector lever in the position “P” of an automatic transmission, so long as the ignition key is removed.
Thus with actuating devices having a mechanical clutch to the gearshift, unintended actuation of the selector lever when the ignition key is removed or the ignition is shut off is prevented, and therewith unintended disengagement of the parking lock in the gearbox, due to which the vehicle could be unintentionally placed in motion.
The shift-lock system represents another example of such a safety function which ensures that shifting out of the “P” or “N” shift position is only possible for safety reasons when the brake pedal is depressed. It also serves the purpose of preventing uncontrolled starting of the vehicle at the moment a drive gear is engaged.
The known, mono-stably constructed, actuating devices also have the disadvantage that the driver must get acquainted with a new operating concept involving a lever that always returns to the center position, whereby this operating concept differs greatly from traditional transmission operation. Furthermore, such mono-stable actuating devices comprise in general a variety of actuators for the selective blockage of unauthorized shift commands depending on the driving condition of the vehicle, which is expensive to construct and entails the corresponding costs.